Aeration | Brown Patch | General Lawn Advice | Lawn Disease
Leaf Spot | Managing Weeds | Perfect Mowing | How to Water

Leaf Spot

The Double Whammy Lawn Disease

Leaf spot and melting out are the common names given to a large number of diseases caused by the same family of fungi. Helminthosporium (now that's a mouthful!) contains a large number of individual disease-causing organisms. What's similar in the diseases of this family is that they give your lawn a real one-two punch by creating the leaf spot phase in the spring and autumn but changing gears into a sheath and root rot phase during the heat of summer.

When You Can Expect To Be Seeing Spots?

The fungi survive the winter as spores (fungus seeds) and as mycelium (fungus strands) in and on diseased turf tissue. When spring temperatures reach 55 to 60 degrees and there is a lot of moisture from rain or dew, the fungus begins to grow and spreads its spores by wind and water. As the weather warms, the disease moves into the second phase of melting out.

Damage Symptoms:

During the leaf spot phase of this disease (spring or autumn), individual grass blades will have large numbers of lesions (or infection marks) that appear a little like a cigarette burn, a dark circle with a tan spot in the centre. During this part of the disease, the lawn takes on a brown under cast making it appear underfed or dried out. Even though leaf spot does not do significant damage to the turf during this phase, it sets the stage for the much more serious melting out phase.

The melting out phase begins during hot, dry weather and causes large irregular areas that may appear dried out. There may not be any distinctly visible symptoms during the melting out phase, as the damaged areas may appear very similar to the effects of dry weather or insect injury.

Early Action Needed - Don't Snooze, You Might Lose

As with all diseases, how the turf is watered, fed and mowed makes a huge difference. Its best to be sure the grass does not stay continuously wet or become excessively dry.

Water no more than once per week and soak the soil to a depth of 6". Water in the morning so the grass will not remain wet for long periods. Open the area around the grass crowns (where the plant goes through the thatch and into the soil) with core aeration. And keep the lawn properly fertilized and regularly aerated. Collecting the clippings during the spring and autumn (leaf spot stage) will help reduce the spread of the disease.

Treatments, if needed, should begin early. Spring and early summer applications of fungicide can be effective, but little can be done to reverse the disease once the melting out phase begins.

Summary

Leaf spot makes turf look sick, but does little permanent damage. However, it sets the stage for the more serious melting out phase of the disease.

Water in the morning so turf can dry out quickly. This helps prevent the spread of leaf spot spores.

Melting out occurs in hot weather and can be easily confused with drought stress or insect damage.

Frequent aeration , and thatch management helps keep turf crowns open and reduces disease activity